This invention relates to a thermal recording apparatus which performs a thermal recording on a thermal recording material using a thermal head.
The thermal recording employing thermal recording materials (hereinafter thermal materials) comprising a thermal recording layer on a side of a substrate such as paper or film has been commonly utilized to record an image produced in diagnosis by ultrasonic scanning.
The thermal recording eliminates the need for wet development processing and offers several advantages including convenience in handling. Hence in recent years, the use of the thermal recording system is not limited to small-scale image recording in such as diagnosis by ultrasonic scanning and an extension to those areas of medical diagnosis such as MRI and X-ray photography where large and high-quality images are required is under review.
The thermal recording apparatus uses a thermal head having a glaze in which heating elements corresponding to the number of pixels of one line are arranged in a main direction and, with the glaze slightly pressed against the thermal recording layer of the thermal material, the two members are moved relative to each other in a sub-direction approximately perpendicular to the main direction, and the respective heating elements in the glaze are heated with provision of recording energy in accordance with an image data of the image to be recorded to heat the thermal recording layer of the thermal material imagewise, thereby accomplishing image reproduction.
The thermal recording apparatus receives the image data from image supply sources such as a CT diagnosis apparatus, an MRI diagnosis apparatus and the like, subjects the received image data to image processing such as sharpness correction and the like for increasing sharpness by emphasizing an outline of the image so as to obtain a clear and impressive image and heats respective heating elements by driving the thermal head in accordance with the image data which has been subjected to image processing to record a thermal image corresponding to the image data inputted from the image data supply source.
The thermal recording apparatus has a problem that, when the image is recorded on the thermal material by the thermal head, the recorded image becomes blurred due to heat diffusion to have basically lower resolution compared with the image recorded on a light sensitive material by such as a laser beam.
To solve this problem compensating a blurred image due to heat, it has been necessary to use a peaking filter or the like for compensating the blur of the image caused by the heat thereby increasing the grade of emphasis on the sharpness of the image to be recorded so that the above-described sharpness correction processing is performed.
However, in an ordinary thermal recording apparatus, necessity of increasing the sharpness by performing the sharpness correction processing as described above caused emphasis of a noise component at the same time or, as shown in FIG. 14, when such as a letter xe2x80x98Hxe2x80x99 was recorded, the outline of the letter xe2x80x98Hxe2x80x99 was in some cases exaggerated to produce a false outline (artifact), depending on an algorithm for sharpness correction processing.
Moreover, when the thermal head with a recording density of about 300 dpi (dots/inch) was used, a scanning line structure which corresponded to coarse-graininess of dots of respective recording pixels in the thermal head became visually recognizable, thereby deteriorating the quality of the recorded image. This decrease of the quality of the recorded image became an obstacle for image observation in an application which required for an intermediate tone with high precision and high quality such as medical diagnosis as described above to bring about a serious problem leading to a diagnosis error.
The present invention has been accomplished under these circumstances and has an object to provide a thermal recording apparatus which is capable of recording a high-quality image that has sufficient sharpness without performing sharpness correction processing and allows a scanning line structure to be visually unrecognizable.
In order to achieve the above object, the invention provides a thermal recording apparatus for two-dimentionally recording the image on a thermal material which moves relatively in a sub-direction approximately perpendicular to a main direction by a thermal head comprising a specified number of heating elements arranged in said main direction, wherein a recording density of said thermal head is 400 dpi or more, and wherein said image is recorded by dividing heat recording points per pixel in said sub-direction into between 2 and 4.
It is preferable that heating duty of a control signal which controls an ON-OFF of said heating element is set between 25% and 50%.
Preferably, a heater width of said heating element in the main direction is between 20 xcexcm and 50 xcexcm, and wherein a heater length of said heating element in the sub-direction is between 30 xcexcm and 60 xcexcm.
Preferably, a coating thickness of a protective layer for coating a surface of said heating element is between 4 xcexcm and 8 xcexcm.
It is further preferable that the recording density of said thermal head is 508 dpi.